[Hydrochemical and Isotopic Characteristics in the Shallow Groundwater of the Fenhe River Basin and Indicative Significance].

The Fenhe River basin is the second largest tributary of the Yellow River. Piper diagrams, Gibbs, PCA, correlation analysis and forward derivation modeling were used to analyze the distribution characteristics and the controlling factors of the groundwater chemistry and stable isotopes in the Fenhe River basin, which revealed the water cycle and water quality evolution process. The results indicated that the groundwater is a weakly alkaline, micro-hard water, the dominant anions and cations are HCO and Ca, the major groundwater types are Mg-Ca-HCO and Mg-Ca-Cl-SO, the groundwater quality is good, and more than 94% of the samples belong to classes Ⅰ-Ⅲ. The average values of D and O of the Fenhe River groundwater are -70.2‰ and -9.6‰, which are similar to the isotope values of the precipitation from July to September, indicating that the groundwater may have originated from this period and that the groundwater recharge mode (dominant flow and piston flow) has a spatial variation. Rock weathering is the dominant source of ions in the groundwater, with an average contribution of 87%, while the contributions of atmospheric input and human activity are 8% and 5%, respectively. For rock weathering, silicate, evaporate, and carbonate rock contribute equally to the groundwater solutes, accounting for 32%, 28%, and 26%, respectively. The results of this study provide the basis for promoting the sustainable development and utilization of groundwater resources in the Fenhe River basin.